The present invention relates to apparatus for recording and reproducing data on a magnetic recording medium, for example a disk or a tape, having a plurality of recording tracks, which are concentric in the case of a disk and parallel in the case of a tape.
The apparatus is of the type that comprises at least one magnetic head and a mechanism for positioning the head with respect to the tracks of the magnetic recording medium.
In known apparatus for recording and reproducing data, each magnetic head is provided either with a single gap for recording and reading the information concerned ("single gap" type), or with two independent gaps, one for recording and one for reading ("read after write" type), disposed in such a way that they are both transverse to the longitudinal axis of the recording track and centered on the axis. In both types, erasing gaps may be disposed at the sides of the recording gap for "cleaning up" the recording signal thereby defining a recording "tunnel".
The width of the recording gap of the head is normally a little smaller than the width of the track of the magnetic recording medium. The width of the tracks determines the packing density of tracks, normally expressed in tracks per inch (t.p.i.).
In the case of magnetic disks of flexible type, which are commercially known by the term "floppy disk", standardised packing densities have been adopted by most manufacturers, so as to make the various items of equipment interchangeable with each other. A very wide-spread packing density is 48 t.p.i. In order to increase the capacity of each individual disk, the packing density has been raised to 96 t.p.i., with a consequential reduction in the width of each track.
The magnetic heads used for reading magnetic recording media with a packing density of 48 t.p.i. have recording and reading gaps of about 317 .mu.m wide, with at the sides, two erasing gaps which are each about 150 .mu.m in width. The magnetic heads which are used for reading magnetic recording media with the packing density of 96 t.p.i. however have reading and recording gaps about 159 .mu.m wide with, at the sides, two erasing gaps which are each about 80 .mu.m in width.
The mechanisms for positioning the head with respect to the disk are therefore controlled in such a way as to move the head by distances which are linked to the packing density. That means that, in the apparatuses for handling disks with a packing density of 48 t.p.i., the stepping movement of the head is over a distance of 529 .mu.m, while in the case of apparatus for dealing with disks with a packing density of 96 t.p.i., the stepping movement of the head is 264.5 .mu.m.
It will be apparent that pre-recorded disks with a packing density of 48 t.p.i. can also be read by apparatus or equipment which have heads and positioning mechanisms that are suitable for handling disks with a packing density of 96 t.p.i., the signal which is prerecorded on a 48 t.p.i. disk being sufficiently wide and strong to be read by the head of the equipment for dealing with 96 t.p.i. disks. However, such 48 t.p.i. disks cannot be recorded by the equipment for dealing with 96 t.p.i. disks and then transferred back into a piece of equipment with 48 t.p.i. disks. The latter would no longer be capable of reading such disks, the signal recorded with a head of the 96 t.p.i. apparatus being too narrow and weak to be correctly read by a head of an apparatus for dealing with 49 t.p.i. disks.